Field of the Invention
The present invention relates to a method and apparatus for electromagnetically discriminating between true and false coins or the like.
True and false coins have been discriminated by a mechanical method such as judging outer diameters for long years, and recently by an electrical method.
An electrical method discriminates between true and false coins by checking the electromagnetic characteristic of a coin falling along a coin passage in a coin discriminating apparatus by using a coin sensor mounted along the coil passage. One type of a coin sensor for discriminating between true and false coins uses exciting means for electromagnetically exciting a coin and means for detecting an electromagnetic response of the excited coin, and analyzes the detected response data. Another type of a coin sensor for discriminating between true and false coins uses a coil of an oscillator circuit mounted at one end of a coin passage to detect a shift of the oscillation frequency when a coil passes near the coil.
FIG. 17 shows an example of a conventional electronic discrimination circuit. This circuit has a first sensor 11 for detecting the electromagnetic characteristic of a coin at its central area, and a second sensor 12 for detecting the electromagnetic characteristic of the coin at its peripheral area. A signal detected by the first sensor 11 is supplied via a first signal generator means 13 and first peak signal generator means 15 to an A/D converter means 17 to be converted into a digital signal. A signal detected by the second sensor 12 is supplied via a second signal generator means 14 and second peak signal generator means 16 to the A/D converter means 17 to be converted into a digital signal. Each digital signal is compared with a reference value from a reference value storage means 32 or 34 at a comparison/discrimination means 31 or 33 in a CPU to discriminate between true and false. The discrimination result is outputted to an AND circuit 35. The AND circuit 35 outputs a logical product of the two electrical success conditions set by the two sensor systems, so that a coin satisfying the two electrical success conditions only is regarded as a true coin. FIG. 18 is a flow chart including steps S1 to S8 for executing the above discrimination operation.
A coin satisfying the two electrical success conditions at their lowest level is obviously regarded as a true coin. However, it has been found empirically that a coin satisfying the two electrical success conditions at their lowest levels should be regarded as a false coin rather than a true coin. Although if a coin satisfies one of the two electrical success conditions at a sufficiently high level, it can be regarded as a true coin.